Question

这是ViewController文件。我在这里按照教程： https://www.appcoda.com/avfoundation-swift-guide/

我不明白错误：

“条件绑定的初始化程序必须具有可选类型，而不是'[AVCaptureDevice]'”

和

“可选类型的值'AVCapturePhotoOutput？'没打开;你的意思是用'！'还是'？'？“

这些错误意味着什么？我该如何修理它们？

  //
//  CameraController.swift
//  AV Foundation
//
//  Created by ben on 5/10/18.
//  Copyright © 2018 Pranjal Satija. All rights reserved.
//

import Foundation
import AVFoundation
import UIKit
class CameraController {
    var previewLayer: AVCaptureVideoPreviewLayer?
    var captureSession: AVCaptureSession?

    var currentCameraPosition: CameraPosition?

    var frontCamera: AVCaptureDevice?
    var frontCameraInput: AVCaptureDeviceInput?

    var photoOutput: AVCapturePhotoOutput?

    var rearCamera: AVCaptureDevice?
    var rearCameraInput: AVCaptureDeviceInput?
}

extension CameraController {
    func displayPreview(on view: UIView) throws {
        guard let captureSession = self.captureSession, captureSession.isRunning else { throw CameraControllerError.captureSessionIsMissing }

        self.previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
        self.previewLayer?.videoGravity = AVLayerVideoGravity.resizeAspectFill
        self.previewLayer?.connection?.videoOrientation = .portrait

        view.layer.insertSublayer(self.previewLayer!, at: 0)
        self.previewLayer?.frame = view.frame
    }

    func prepare(completionHandler: @escaping (Error?) -> Void) {
        func createCaptureSession() {
            self.captureSession = AVCaptureSession()
        }

        func configureCaptureDevices() throws {
            let session = AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInWideAngleCamera], mediaType: AVMediaType.video, position: .unspecified)
            guard let cameras = (session.devices.flatMap { $0 }), !cameras.isEmpty else { throw CameraControllerError.noCamerasAvailable }

            for camera in cameras {
                if camera.position == .front {
                    self.frontCamera = camera
                }

                if camera.position == .back {
                    self.rearCamera = camera

                    try camera.lockForConfiguration()
                    camera.focusMode = .autoFocus
                    camera.unlockForConfiguration()
                }
            }
        }

        func configureDeviceInputs() throws {
            guard let captureSession = self.captureSession else { throw CameraControllerError.captureSessionIsMissing }

            if let rearCamera = self.rearCamera {
                self.rearCameraInput = try AVCaptureDeviceInput(device: rearCamera)

                if captureSession.canAddInput(self.rearCameraInput!) { captureSession.addInput(self.rearCameraInput!) }

                self.currentCameraPosition = .rear
            }

            else if let frontCamera = self.frontCamera {
                self.frontCameraInput = try AVCaptureDeviceInput(device: frontCamera)

                if captureSession.canAddInput(self.frontCameraInput!) { captureSession.addInput(self.frontCameraInput!) }
                else { throw CameraControllerError.inputsAreInvalid }

                self.currentCameraPosition = .front
            }

            else { throw CameraControllerError.noCamerasAvailable }
        }

        func configurePhotoOutput() throws {
            guard let captureSession = self.captureSession else { throw CameraControllerError.captureSessionIsMissing }

            self.photoOutput = AVCapturePhotoOutput()
            self.photoOutput!.setPreparedPhotoSettingsArray([AVCapturePhotoSettings(format: [AVVideoCodecKey : AVVideoCodecJPEG])], completionHandler: nil)

            if captureSession.canAddOutput(self.photoOutput) { captureSession.addOutput(self.photoOutput) }
            captureSession.startRunning()
        }

        DispatchQueue(label: "prepare").async {
            do {
                createCaptureSession()
                try configureCaptureDevices()
                try configureDeviceInputs()
                try configurePhotoOutput()
            }

            catch {
                DispatchQueue.main.async {
                    completionHandler(error)
                }

                return
            }

            DispatchQueue.main.async {
                completionHandler(nil)
            }
        }
    }
}

extension CameraController {
    enum CameraControllerError: Swift.Error {
        case captureSessionAlreadyRunning
        case captureSessionIsMissing
        case inputsAreInvalid
        case invalidOperation
        case noCamerasAvailable
        case unknown
    }

    public enum CameraPosition {
        case front
        case rear
    }
}

Answer 1

在您的一条评论中，您最终指出哪条线导致错误：

guard let cameras = (session.devices.flatMap { $0 }), !cameras.isEmpty else { throw CameraControllerError.noCamerasAvailable }

这有几个问题。正如您在Swift手册的Control Flow - Early Exit部分中所看到的，guard let用于验证可选变量不是nil。

错误告诉您表达式(session.devices.flatMap { $0 })不是可选的。实际上，这里使用flatMap毫无意义，因为session.devices是一个非可选值数组（[AVCaptureDevice]]）。

您应该将guard重写为：

guard !session.devices.isEmpty else {
    throw CameraControllerError.noCamerasAvailable
}

然后循环变为：

for camera in session.devices {

试图制作一个相机应用程序，是Swift的新手

1 个答案: